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Enveloped by Sails of Glass – the Fondation Louis Vuitton in Paris
17, 18 A xonometry of a joint of the glulam truss and the steel connecting elements 19 Actual joint 20 Details of the verriere and its wood secondary structure 21 Air space between verrieres and the building massing
2015 ¥ 1 ∂
Matt King is partner in the engineering firm T/E/S/S. From the very first sketches, King was involved in the technological development of the Fondation Louis Vuitton; he prompted the team to develop the large glass sails that envelop the building. In 2012 he received the “Grand Prix National de l’Ingénierie”. Jaques Raynaud is an architect and engineer and was responsible for the geometry and technical configuration of the glass sails. After accruing more than 20 years’ experience in the development of complex structures and facades at the RFR Group, an engineering firm, he established its Department of Structural Design, which develops optimised solutions for extraordinary architecture.
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The majority of the elements are only curved in one plane, but at the intersection between surfaces, a more complex twisting, doubly curved geometry is generated. These sections are fabricated by producing a curved planar beam, then cutting it into 25 mm thick slices and re-gluing these together on a jig with the required curvature in the other axis. The section is then finished using a computer-controlled five-axis milling machine. The glulam approach can also generate higher-strength sections, as each individual plank can be graded and specifically chosen, creating a more uniform section less prone to natural defects in the wood. Relatively high-strength GL28
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timber was produced in this way, sourcing the planks from high-altitude forests in Austria, and only employing planks with a high density ranging from 500 to 700 kg/m3, and an average density of 585 kg/m3. To reduce the risk of fissuring and splitting of the timber over time the moisture content of the timber was also carefully controlled. Over a period of years the moisture content of external, sheltered timber in the Paris climate will settle down to around 14 %. For the project, all of the planks were pre-dried to a controlled moisture content of 9 % to 14 %. This ensures that the timber’s moisture content will tend to increase over its lifespan, reducing the risk of fissuring due to drying. The fabrication process adopted for the double-curved beams also has the advantage of introducing glue planes close to the surface in both directions. This tends to slow down changes in moisture content of the section, making it less sensitive to cyclical changes in the external environment, both reducing the risk of fissuring, and limiting crack depth to the outer layer of timber. In the end, this form of double lamination was adopted even for the planar curved elements to enhance their durability and resistance to fissuring. In timber design the connections are typically the system’s most critical elements, 20 and this was certainly true of this project. The nature of the structure meant that connections had to be continuous, transferring principal loads in the strong direction for timber (axial and bending forces in the direction of the grain). However, due to the structure’s geometrical complexity, eccentricities were inevitable, and these tended to introduce additional secondary torsional and bending forces. The classic connection detail involves slotting a vertical steel plate into the timber section and linking the two with a grid of 16 mm diameter transversal pins. This approach had to be adapted to incorporate two plates in order to generate the push-pull necessary to transfer the secondary torsion and bending forces. This technique required high-precision fabrica- 21
tion so that the pre-drilled holes for the pins in the timber aligned perfectly with those in the twin plates. Stainless steel was used in all of the pins and plates to ensure maximum durability of the assembly. The theoretical strength of the connections was then justified by full-scale testing. Both the construction system selected and the detailing and execution of the verrieres for the Fondation Louis Vuitton support the architect’s intention to create a rich and varied experience combining contemporary art display with a strong connection to the surrounding woods and the Jardin d’Acclimatation.